Systems have been developed to obtain an auditory evoked response (AER) or brainstem auditory evoked response (BAER) for a patient representing activity of the patient's auditory system. The AER is an electrical brain wave or neural response obtained from electrodes placed on the patient in response to a stimulus, normally a sound. Depending on the latency of the response and the placement of the electrodes, different classes or types of AERs can be obtained. Those with the shortest latency are generated by the inner ear and the auditory nerve, and are referred to as electrocochleography (“ECOG” or “ECochG”) responses. The next response reflects activity within the auditory brainstem and is referred to as an auditory brainstem response (ABR). Further detail is provided in Hall, James W, III; Handbook of Auditory Evoked Responses; Allyn and Bacon; Needham Heights, Mass., 1992.
Electrocochleography systems are currently used to perform diagnoses of the cochlea and vestibular apparatus. In the case of the vestibular system, recently analysis for this specific part of the ear has been referred to as electrovestibulography (EVestG), being a distinct variant of ECOG. The systems are used to produce a patient neural response which involves placing a recording electrode as close as practical to a patient's cochlea. An acoustic transducer, eg an earphone, is used to provide an auditory stimulus to evoke the response. For EVestG the patient is however tilted, in different directions, to evoke a specific response from the vestibular apparatus. It is not necessary to also use an auditory stimulus for EVestG. A distinct EVestG signal, similar to an ECOG signal but representing the neural response from the vestibular apparatus, is used to determine an Sp/Ap ratio that can be used for the diagnosis of a number of conditions, particularly Meniere's disease. The first wave, normally labelled N1, of the response signal is examined to determine the summating potential (Sp), the action potential (Ap) and the second summating potential (Sp2), as shown in FIG. 1. The response is only of the order of a few μV and is received with considerable unwanted noise making it difficult to determine and isolate.
International patent publication WO 2006/024102 to Monash University describes an ECOG system to extract neural event data that can be used to indicate whether a person has Meniere's, Parkinson's disease or depression. The system produces biological marker data representing the Sp/Ap ratio and a TAP marker that can be used to indicate the presence of a disorder. To assist with identification of a wide variety of neurological and neurodegenerative disorders it would be advantageous to provide at least a useful alternative or in particular a system that is able to provide additional biological marker data for a person that can be used for different disorders.